1. Field of the Invention
The present invention relates to a center mechanism of a tire vulcanizing press wherein a bladder is held by the center mechanism adapted to be vertically moved at the center of the press, and more particularly to such a center mechanism wherein downward projection of the center mechanism can be suppressed by modifying the arrangement of a cylinder unit.
2. Description of the Related Art
FIG. 3 shows a conventional center mechanism of a tire vulcanizing press, wherein a green tire T is set on a lower mold 53 fixed through a lower-mold mounting member 52 on a base frame 51 by a vertically movable loader 55 having a chuck 54 to carry out shaping of the green tire T. A center mechanism 58 is provided through a guide sleeve 59 at a central portion of the lower-mold mounting member 52. The center mechanism 58 includes a lift member 60 vertically movably inserted through the guide sleeve 59, a center post 61 vertically movably inserted through the lift member 60, a first cylinder unit 63 located under the lift member 60 and having a piston rod 63a adapted to be advanced upwardly, and two second cylinder units 64 located on opposite sides of the first cylinder unit 63 and having piston rods 64a adapted to be advanced downwardly. A bottom ring 68 for holding a lower portion of a bladder 67 is supported to the upper end of the lift member 60, and a top ring 69 for holding an upper portion of the bladder 67 is supported to the upper end of the center post 61. The lower ends of the piston rods 64a of the second cylinder unit 64 are connected to the lower end of the first cylinder unit 63 by a connecting member 72. The lift member 60 is lowered or lifted together with the center post 61 by advancing or retracting the piston rods 64a of the second cylinder units 64, respectively. Further, the center post 61 only is lifted or lowered by advancing or retracting the piston rod 63a of the first cylinder unit 63, respectively.
The operation of the center mechanism of the tire vulcanizing press mentioned above will now be described. The bladder 67 is stretched in a vertical direction on the center line of the lower mold 53 as shown by a dots-dash line in FIG. 3 by lowering the lift member 60 to its lower limit position and lifting the center post 61 to its upper limit position. Then, the loader 55 with the chuck 51 grasping the green tire T is lowered to set the green tire T on the lower mold 53. After the green tire T is set on the lower mold 53, a pressure fluid such as stream or hot gas is introduced into the bladder 67 to expand it. During expansion of the bladder 67, the center post 61 is lowered to thereby lower the top ring 69. Thus, the bladder 67 is gradually deformed so as to fit on the inner surface of the green tire T. Finally, the bladder 67 is entirely brought into close fit with the inner surface of the green tire T, thereby performing the shaping of the green tire T. After completion of the shaping, an upper mold (not shown) is lowered to be fitted to the lower mold 53 to carry out vulcanizing of the green tire T.
After completion of the vulcanizing, the upper mold is lifted. Then, the lift member 60 is lifted together with the center post 61 to thereby separate and lift the vulcanized tire T from the lower mold 53. Then, the center post 61 is lifted and the lift member 60 is lowered to thereby separate and draw out the bladder 67 closely fitted with the inner surface of the vulcanized tire T. Finally, the vulcanized tire T is taken out of the tire vulcanizing press by a carrier member (not shown), thus completing one cycle of vulcanization.
In the center mechanism 58 of the tire vulcanizing press mentioned above, the first cylinder unit 63 for vertically moving the center post 61 only with respect to the lift member 60 is located in tandem under the lift member 60 in such a manner that the piston rod 63a is adapted to be advanced upwardly. Accordingly, the first cylinder unit 63 and the second cylinder units 64 located on the opposite sides of the first cylinder unit 63 are largely projected downward from the base frame 51. In this circumstance, in installation of the tire vulcanizing press, a deep pit 75 is dug in a floor to store the cylinder units 63 and 64. However, the deeper such a pit, the higher a cost required for foundation work. Further, in transportation of the tire vulcanizing press, the cylinder units 63 and 64 projecting downwardly from the base frame 51 cause a hindrance, and it is therefore necessary to prepare a special stand for the transportation.